Transforming growth factors (TGFs) are hormonally active polypeptides capable of inducing a transformed phenotype when added to normal, non-neoplastic cells. TGFs are found in certain normal tissues and in many retrovirally-transformed and tumor-derived cell lines. The first aim of this project was to identify and isolate TGFs produced by transformed cells. We have found that culture fluids from feline sarcoma virus-transformed cells contain two different factors, eTGF and beta-TGF that, when acting in combination, induce acute phenotypic transformation in rat fibroblasts. Both factors have been purified to homogeneity and characterized. eTGF is a 6.0 kilodalton polypeptide with limited (25%) amino acid sequence homology to epidermal growth factor (EGF). eTGF and EGF, both termed alpha-TGFs, are potent mitogens which, when acting alone, have weak transforming action. The transforming activity of alpha-TGFs is strongly potentiated by beta-TGF. Beta-TGF purified from the same cell line that produces eTGF is a 23 kilodalton, disulfide-linked dimer that consists of two 11 to 12 kilodalton subunits. Beta-TGF does not induce phenotypic transformation when acting alone. In addition to its ability to synergize with alpha-TGFs, beta-TGF is a potent mitogen for normal cells in monolayer culture. Our second aim was to identify the cell surface receptors mediating the action of TGFs. We have identified the receptor for eTGF as being the same as the receptor for EGF, a 150 to 170 kilodalton membrane glycoprotein with associated tyrosine kinase activity. Despite their limited structural homology, eTGF and EGF exhibit similar affinity for binding to this receptor type and a similar potency to activate the receptor-associated protein tyrosine kinase and to down-regulate the receptor. It has been found that the EGF/eTGF receptor is a target for rapid modulation by beta-TGF. We are currently addressing the kinetic and structural properties of receptors for beta-TGF and testing the hypothesis that beta-TGF induces structural and functional changes in the EGF/eTGF receptors. (J)